This study will provide information relative to the 3 conceptual elements needed for control of differential gene expression in vertebrates, namely, control genes, structural genes, and effectors. Heterokaryon complementation analyses will identify the existence of control elements and their hierarchy of expression in the pigment cell. Electrophoretic comparisons (2-D) will help distinguish control and structural genes from each other. Extinction-activation experiments will localize the effectors (nucleus or cytoplasm) and their type of action (inhibitory or stimulatory). Experiments will be executed using primary cultured neural crest derived melanocytes from chick embryos. Seven mutant stocks will be used. Heterokaryons will be formed using inactivated Sendai virus and identified autoradiographically. Extinction-activation experiments will utilize various fused combinations of minicells, cytoplasts and whole cells.